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Swift/XRT follow-up observations of three unidentified INTEGRAL sources

ATel #3078; R. Landi, A. Malizia (INAF/IASF Bologna), A. Bazzano, M. Fiocchi (INAF/IASF Rome), A. J. Bird (Univ. Southampton), N. Gehrels (NASA/GSFC), D. N. Burrows (PSU)
on 14 Dec 2010; 17:02 UT
Credential Certification: Raffaella Landi (landi@iasfbo.inaf.it)

Subjects: X-ray, Gamma Ray, Request for Observations

We report the results of X-ray follow-up observations performed with Swift/XRT of three unidentified INTEGRAL sources listed in the 4th IBIS Survey Catalogue (Bird et al. 2010, ApJS, 186, 1).

IGR J02115-4407

There are three sources detected by XRT within the IBIS positional uncertainty (none of them are detected above 3 keV):

Source #1: it is detected at 4 sigma c.l. (0.3-10 keV) and is located at R.A.(J2000) = 02h 11m 44.03s and Dec.(J2000) = -44d 07m 00.3s (5.8 arcsec uncertainty). It has a counterpart in a USNO-A2.0 object (USNO-A2.0 0450_00755064) with magnitudes R ~17.9, and B ~18.9; no infrared counterpart is found for this object; in NED, it is associated with the galaxy APMUKS(BJ)B020945.22-442104.8. The X-ray data are described by a power law with photon index ~1.9 and a 2-10 keV flux of 1.1 x 10-13 erg cm-2 s-1.

Source #2: is detected at 3.1 sigma c.l. (0.3-10 keV) and its position is at R.A.(J2000) = 02h 11m 20.0s and Dec.(J2000) = -44d 07m 37.5s (6 arcsec uncertainty). It coincides with a USNO-A2.0 object (USNO-A2.0 0450_00752627) having magnitude R ~17.9, and B ~19.1. The source has no counterpart in the 2MASS catalogue. From X-ray data we can only infer a 2-10 keV flux of 5.8 x 10-14 erg cm-2 s-1, assuming a power law with photon index 1.8.

Source #3: is detected at 2.4 sigma c.l. (0.3-10 keV) and has coordinates R.A.(J2000) = 02h 11m 33.4s and Dec.(J2000) = -44d 11m 10.3s (7 arcsec uncertainty). No counterpart at other wavelengths is found for this object; the 2-10 keV flux is 3.7 x 10-14 erg cm-2 s-1, assuming a power law with photon index 1.8.

All three sources are most likely associated with the galaxy group LCLG-45078 at z = 0.104; it is not clear at this stage if the IBIS source is the galaxy group or one of its members.

IGR J16443+0131

Just at the border of the IBIS error circle, we find an X-ray source detected at 4.4 sigma c.l. in the 0.3-10 keV energy band (no detection above 3 keV) and positioned at RA(J2000) = 16h 44m 38.1s and Dec(J2000) = +01d 29m 03.5s (6 arcsec uncertainty). Within the XRT positional uncertainty we find a USNO-B1.0 object (R ~18.5, and B ~20), which is also reported in the 2MASS catalogue (J ~16.8, H ~15.9, and K ~15.1). The XRT location is also compatible with a radio source (NVSS J164437+012903) having a 20 cm flux of 7.2+/-0.5 mJy. The X-ray spectroscopy provides a 2-10 keV flux of 2.7 x 10-13 erg cm-2 s-1, assuming a power law with photon index 1.8.

The X-ray/radio detection together with the high location far above the Galactic plane, suggests that this is an AGN.

IGR J18457+0244

Within the IBIS error circle XRT detects one X-ray source (at 3.9 sigma c.l. in the 0.3-10 keV), which is still observed above 3 keV at 3.6 sigma c.l.. It is located at RA(J2000) = 18h 45m 40.1s and Dec.(J2000) = +02d 42m 07.3s (6 arcsec uncertainty). The XRT position is compatible with two 2MASS objects having comparable magnitude J ~16, H ~15, and K ~15. No counterpart is found at other wavelengths. The X-ray spectroscopy indicates an absorbed power law spectrum (Gamma = 1.8, NH ~3 x 1023 cm-2) and a 2-10 keV flux of 8.3 x 10-13 erg cm-2 s-1.